For the second time in American history, the president's online portal switched owners.

Out went the photographs of former president George W. Bush, which were posted until noon Tuesday. As the government officially changed hands, the presidential Web site WhiteHouse.gov began to serve the online vision and agenda of President Obama.

According to the site's first blog post, written by Macon Phillips, a veteran of Obama's campaign and now the White House's new-media director, WhiteHouse.gov "will serve as a place for the President and his administration to connect with the rest of the nation and the world."

The top three priorities of the site, Phillips wrote, are "communication," "transparency" and "participation" -- buzz words in online social networking circles. Visually, the site is a close cousin of the campaign Web site BarackObama.com and the presidential transition portal Change.gov. And just as Obama maintained an active YouTube presence during his 21-month campaign and nearly three-month transition, he will do so as president. WhiteHouse.gov added a YouTube channel shortly after Obama took office and is promising weekly video addressees.

Steve Grove, YouTube's head of news and politics, cheered the move. "By bringing the White House onto YouTube just moments after the inauguration, the Obama administration has demonstrated a commitment to a transparent government that connects directly with citizens," he said.

Among other new features, WhiteHouse.gov now also makes this pledge: It will post all non-emergency legislation online for five days, allowing the public to review and comment on proposed laws before Obama signs them.

-- Jose Antonio Vargas and Sarah Cohen

THREAT 'UNCERTAIN'

Security Alert Issued For Inauguration Day

U.S. counterterrorism officials said they aggressively investigated a potential threat of "uncertain credibility" to Tuesday's inauguration events posed by an East African Islamist group with ties to al-Qaeda.

In a bulletin issued Monday night to state and local law enforcement, the FBI, the Department of Homeland Security and intelligence officials said they were analyzing recent information that people affiliated with al-Shabaab, a radical group fighting an insurgency in Somalia, might try to stage an attack Tuesday, U.S. officials said.

Analysts had drawn no conclusions but were examining the possibility of a link between the threat and reports that U.S.-based Somalis have traveled to the African country to fight.

"Authorities at all levels are vigorously pursuing any lead relating to this threat information," DHS spokesman Russ Knocke said, saying that Obama administration officials were informed of the investigation. "The transition team has been briefed and is fully integrated into the process."

Another U.S. counterterrorism official said Tuesday that intelligence agencies were "not dismissive" of the threat but stressed the lack of corroboration and detail. The tip appears to have originated with U.S. law enforcement agencies, as opposed to overseas operatives.

The State Department designated al-Shabaab a terrorist group in February, citing "a number" of al-Qaeda affiliates among its members and its responsibility for numerous attacks in the past two years aimed at undermining the Somali government and replacing it with one based on Islamic law. Kenya has recently accused the group of threatening "jihad," or holy war, against Nairobi for its support of the Somali government.

Last fall, the FBI returned the remains of college student Shirwa Ahmed to his family in the Minneapolis area. Authorities would not say if he was a suspect or a victim, but community members have said the naturalized U.S. citizen blew himself up in a suicide bombing in northern Somalia in late October. The FBI is investigating the disappearance of more than a dozen young men from that Minnesota area.

While security alerts from Washington are not unusual, ones with even the "limited specificity" of the al-Shabaab notice are atypical. Knocke noted that security for the inauguration was at unprecedented levels.

-- Spencer S. Hsu

THE VERY DEEP SOUTH

Scientists Celebrate Obama From Afar

In what may well be the farthest-flung celebration of President Obama's inauguration, scientists aboard the U.S. research vessel Laurence M. Gould held a commemoration Tuesday 10,000 miles from Washington -- off Antarctica.

The researchers, who are spending three days at sea examining signs of climate change, decided to call the temporary study area they have established Ocean Station Obama.

Doug Martinson, an oceanographer at Columbia University's Lamont-Doherty Earth Observatory and the cruise's chief scientist, said they named the station after the 44th president and his administration "to recognize their vital interest in the problem of climate change."

"The setting of our study, in an area of rapidly changing climate and ecology, is an appropriate spot and moment in our history to dedicate this sampling station to the events taking place in Washington," Martinson said in a statement. "In doing so, we hope to bring ocean sciences and climate change research to the public's attention."

The three-day cruise is a part of a seven-week oceanographic expedition known as the Palmer, Antarctica Long-Term Ecological Research project, which has surveyed a section of the western Antarctic Peninsula each year since 1993.